A major goal of biomedical research has been the identification of molecular mechanisms that can enhance memory. Here we report a novel signaling pathway that regulates the conversion from short- to long-term memory. The mTOR complex 2 (mTORC2), which contains the key regulatory protein Rictor (Rapamycin-Insensitive Companion of mTOR), was discovered only recently, and little is known about its physiological role. We show that conditional deletion of rictor in the postnatal murine forebrain greatly reduces mTORC2 activity and selectively impairs both long-term memory (LTM) and the late (but not the early) phase of hippocampal long-term potentiation (LTP). Actin polymerization is reduced in the hippocampus of mTORC2-deficient mice and its restoration rescues both L-LTP and LTM. More importantly, a compound that selectively promotes mTORC2 activity converts early-LTP into late-LTP and enhances LTM. These findings indicate that mTORC2 could be a novel therapeutic target for the treatment of cognitive dysfunction.

Membrane trafficking pathways must be exquisitely coordinated at synaptic terminals to maintain functionality, particularly during conditions of high activity. We have generated null mutations in the Drosophila homolog of pallidin, a central subunit of the biogenesis of lysosome-related organelles complex-1 (BLOC-1), to determine its role in synaptic development and physiology. We find that Pallidin localizes to presynaptic microtubules and cytoskeletal structures, and that the stability of Pallidin protein is highly dependent on the BLOC-1 components Dysbindin and Blos1. We demonstrate that the rapidly recycling vesicle pool is not sustained during high synaptic activity in pallidin mutants, leading to accelerated rundown and slowed recovery. Following intense activity, we observe a loss of early endosomes and a concomitant increase in tubular endosomal structures in synapses without Pallidin. Together, our data reveal that Pallidin subserves a key role in promoting efficient synaptic vesicle recycling and re-formation through early endosomes during sustained activity.

Alcohol activates reward systems through an unknown mechanism, in some cases leading to alcohol abuse and dependence. Herein, we utilized a two-choice Capillary Feeding assay to address the neural and molecular basis for ethanol self-administration in Drosophila melanogaster. Wild-type Drosophila demonstrates a significant preference for food containing between 5 and 15% ethanol. Preferred ethanol self-administration does not appear to be due to caloric advantage, nor due to perceptual biases, suggesting a hedonic bias for ethanol exists in Drosophila. Interestingly, rutabaga adenylyl cyclase expression within intrinsic mushroom body neurons is necessary for robust ethanol self-administration. The expression of rutabaga in mushroom bodies is also required for both appetitive and aversive olfactory associative memories, suggesting that reinforced behavior has an important role in the ethanol self-administration in Drosophila. However, rutabaga expression is required more broadly within the mushroom bodies for the preference for ethanol-containing food than for olfactory memories reinforced by sugar reward. Together these data implicate cAMP signaling and behavioral reinforcement for preferred ethanol self-administration in Drosophila melanogaster.

Regeneratable antioxidant property of nanoceria has widely been explored to minimize the deleterious influences of reactive oxygen species. Limited information is, however, available regarding the biological interactions and subsequent fate of nanoceria in body fluids. This study demonstrates a surprising dissolution of stable and ultrasmall (4 nm) cerium oxide nanoparticles (CeO2 NPs) in response to biologically prevalent antioxidant molecules (glutathione, vitamin C). Such a redox sensitive behavior of CeO2 NPs is subsequently exploited to design a redox responsive drug delivery system for transporting anticancer drug (camptothecin). Upon exposing the CeO2 capped and drug loaded nanoconstruct to vitamin c or glutathione, dissolution-accompanied aggregation of CeO2 nanolids unleashes the drug molecules from porous silica to achieve a significant anticancer activity. Besides stimuli responsive drug delivery, immobilization of nanoceria onto the surface of mesoporous silica also facilitates us to gain a basic insight into the biotransformation of CeO2 in physiological mediums.

The loss of heterotrimeric G(o) signaling through the expression of pertussis toxin (PTX) within either the α/β or γ lobe mushroom body neurons of Drosophila results in the impaired aversive olfactory associative memory formation. Herein, we focus on the cellular effects of G(o) signaling in the γ lobe mushroom body neurons during memory formation. Expression of PTX in the γ lobes specifically inhibits G(o) activation, leading to poor olfactory learning and an increase in odor-elicited synaptic vesicle release. In the γ lobe neurons, training decreases synaptic vesicle release elicited by the unpaired conditioned stimulus -, while leaving presynaptic activation by the paired conditioned stimulus + unchanged. PTX expression in γ lobe neurons inhibits the generation of this differential synaptic activation by conditioned stimuli after negative reinforcement. Hyperpolarization of the γ lobe neurons or the inhibition of presynaptic activity through the expression of dominant negative dynamin transgenes ameliorated the memory impairment caused by PTX, indicating that the disinhibition of these neurons by PTX was responsible for the poor memory formation. The role for γ lobe inhibition, carried out by G(o) activation, indicates that an inhibitory circuit involving these neurons plays a positive role in memory acquisition. This newly uncovered requirement for inhibition of odor-elicited activity within the γ lobes is consistent with these neurons serving as comparators during learning, perhaps as part of an odor salience modification mechanism.

No abstract

The brain mechanisms by which animals deal with multiple experiences to predict outcomes are not yet fully understood. We explored the choice strategies that flies use to assess degrees of disadvantage, as well as how flies weigh past and recent experiences to guide decisions. Drosophila were exposed to two conditioning events in a T-maze: an odor paired with an electric shock followed by a second odor paired with an electric shock of a different intensity. Subsequently, flies were forced to choose between the two odors. We found that flies chose to avoid the more 'dangerous' odor by a linear subtraction mechanism that was based on two coexisting memories. We also found that flies weighed experiences of the same danger level (60 V electric shocks) according to the times when the experiences had occurred. More recent experiences had a greater impact and past experiences gradually became 'overlooked' during decisions as the time delay between the two events lengthened. However, the past memory was not so much disrupted as it was overshadowed by recent memories during decisions. Finally, when a past experience was more disadvantageous, wild-type flies were able to coordinate both the temporal factor and the degree of disadvantage into their decisions. By contrast, amnesiac mutant flies made choices completely according to the temporal factor, ignoring the degree of disadvantage. Taken together, wild-type flies are able to store multiple olfactory memories and can coherently evaluate learned experiences to guide their decisions according to the degree of disadvantage and/or the temporal factor.

Heterotrimeric G(o) is an abundant brain protein required for negatively reinforced short-term associative olfactory memory in Drosophila. G(o) is the only known substrate of the S1 subunit of pertussis toxin (PTX) in fly, and acute expression of PTX within the mushroom body neurons (MB) induces a reversible deficit in associative olfactory memory. We demonstrate here that the induction of PTX within the a/b and g lobe MB neurons leads to impaired memory acquisition without affecting memory stability. The induction of PTX within these MB neurons also leads to a significant defect in an optimized positively reinforced short-term memory paradigm; however, this PTX-induced learning deficit is noticeably less severe than found with the negatively reinforced paradigm. Both negatively and positively reinforced memory phenotypes are rescued by the constitutive expression of G(o)a transgenes bearing the Cys 351 Ile mutation. Since this mutation renders the G(o) molecule insensitive to PTX, the results isolate the effect of PTX on both forms of olfactory associative learning to the inhibition of the G(o) activation.